Currently, a technology for processing Media Access Control (MAC) protocol data unit (PDU) is known. In this technology, a MAC PDU includes a plurality of sub-PDUs, each sub-PDU carries a logical channel identifier (LCID), and a communications protocol specifies processing manners corresponding to a plurality of types of LCIDs. Therefore, each sub-PDU may be parsed based on an LCID carried in the sub-PDU.
With the development of communications technologies, releases of the communications protocol change constantly, and processing manners corresponding to LCIDs and specified in different releases of the communications protocol may be different. For example, for an LCID #α, no processing manner corresponding to the LCID #α is defined in one communications protocol release (which is referred to as a communications protocol release #1 below for the convenience of understanding and description). To be specific, for a communications device (which is marked as a communications device #1 below for the convenience of understanding and distinguishing) using the communications protocol release #1 in a network, a value of the LCID #α is an invalid value or a reserved value. In addition, a processing manner corresponding to the LCID #α is defined in another communications protocol release (which is, for example, an updated communications protocol release compared with the communications protocol release #1, and is referred to as a communications protocol release #2 below for the convenience of understanding and description). To be specific, for a communications device (which is marked as a communications device #2 below for the convenience of understanding and distinguishing) using the communications protocol release #2 in a network, the value of the LCID #α is a valid value.
In this case, when the communications device #1 communicates with the communications device #2, the communications device #2 may generate a sub-PDU carrying the LCID #α, and send the sub-PDU to the communications device #1. Because the value of LCID #α is a reserved value or an invalid value for the communications device #1, an error may occur when the sub-PDU carrying the LCID #α is parsed, and as a result, the communications device #1 cannot determine how to process an entire MAC PDU.